Weathering: Processes of Change

1. Weathering:Processes of Change Weathering chemical weathering mechanical weathering moving water erosion ice deposition waves gravity wind glaciers Acids abrasion

2. EQ: How does weathering occur?

3. Describe three ways abrasion occurs in nature. List three things that cause chemical weathering of rocks. Describe the similarity in the ways tree roots and ice mechanically weather rock. Describe five (5) sources of chemical weathering. Weathering

4. The Processes of Change

5. Processes of Change (5) • Weathering and erosion wear down, deposition fills in Earth’s surface. • Weathering is the slow wearing away or breaking down of objects exposed to Earth’s atmosphere • Two kinds of weathering act on Earth’s surface • Mechanical weathering • Chemical weathering

6. Weathering • Weathering is the process by which rock materials are broken down by the action of physical or chemical processes. • Mechanical weathering is the breakdown of rock into smaller pieces by physical means. (ice, wind, water, gravity, plants, animals) • Chemical weathering is the process by which rocks break down as a result of chemical reactions. Water, weak acids, and air can cause chemical weathering.

7. Mechanical Weathering (4) • When objects are broken down into small pieces but their chemical makeup doesn’t change • Wind and moving water are two main causes of mechanical weathering • Repeated changes in temperature (freeze, melt, freeze, melt again)

8. Chemical Weathering (5) • Material of an object is changed • Produces underground caverns • Statue of Liberty needed repairs because of chemical weathering • Examples: • Rust (oxidation) • Acid rain precipitation

9. Erosion (5) • The natural moving of material from one place to another • Erosion transportsweathered rock material • Causes of Erosion: • Moving water • Gravity • Wind • Glaciers (moving rivers of ice) • Waves

10. Deposition (5) • Land torn down in one place is “deposited” in another place • Gravity can cause a landslide moving mud, rock and soil down a hill • Wind erosion can move sand and deposit it in another area • Glaciers (rivers of ice) scrape rocks off the land and moves them downhill

11. Glaciers will stop moving and even retreat and cut a steep U-shaped valley in the land

12. Erosion caused by mountain rivers form V-shaped valleys

13. Hurricanes create waves that erode beaches and cliffs

14. Breaking of waves on a beach can wear it away. The larger the waves, the faster is the rate of erosion.

15. 6 Agents of Mechanical Weathering • 1. Water– as rocks and pebbles roll along the bottom of flowing water, they bump and scrape against each other, causing these rocks to become rounded and smooth. • 2. Wind– wind blows sand and silt against exposed rock eventually wearing away the rock’s surface. • 3. Gravity – rocks grind against each other during a rock slide, creating smaller and smaller rock fragments. Anytime one rock hits another rock, abrasion takes place.

16. Abrasion • Abrasion – the grinding and wearing away of rock surfaces through mechanical action of other rock or sand pebbles. • The three ways that can cause abrasion are wind, water, and gravity.

17. The Causes of Abrasion

18. Frost Action • 4. Ice – water seeps into cracks during warm weather. When the temperature drops, the water freezes and expands, causing the ice to pushagainst the sides of the crack. This causes the crack in the rock to widen eventually braking the rock apart.

19. Ice Wedging

20. Plants and Animals • 5. Some plants can easily break rocks. The roots grow through existing cracks in rocks. The growth causes the root to expand, forcing the crack to widen. The force can eventually split the rock apart. • 6. Animalsthat live in the soil (moles, prairie dogs, insects, worms, gophers), cause a lot of weathering. By burrowing in the ground, these living creatures brake up soil and loosen rocks to be exposed to further weathering.

21. Weathering: Plants and Animals

22. Agents of Mechanical Weathering The breaking down of rock through physical means

23. Flowing Water As rocks and pebbles roll along the bottom of flowing water, they bump and scrape against each other, causing these rocks to become rounded and smooth.

24. WIND wind blows sand and silt against exposed rock eventually wearing away the rock’s surface.

25. GRAVITY Rocks grind against each other during a rock slide, creating smaller and smaller rock fragments. Anytime one rock hits another rock, abrasion takes place.

26. ICE Water seeps into cracks during warm weather. When the temperature drops, the water freezes and expands, causing the ice to push against the sides of the crack. This causes the crack in the rock to widen.

27. Animals Animals that live in the soil (moles, prairie dogs, insects, worms, gophers), cause a lot of weathering. By burrowing in the ground, these living creatures break up soil and loosen rocks to be exposed to further weathering

28. PLANTS The roots grow through existing cracks in rocks. The growth causes the root to expand, forcing the crack to widen. The force can eventually split the rock apart.

29. 3 Agents of Chemical Weathering • These (3) agents weaken the bonds between minerals grains of the rock.

30. 3 Agents of Chemical Weathering • 1. Water – can cause rock to be broken down and dissolve. Can take thousands of years to take place. • 2. Air – the process of oxidation is a chemical reaction in which an element (iron) combines with oxygen, causing rust. • 3. Weak Acids – Includes: • acids in precipitation • acids in Groundwater • acids in living things

31. Weak Acids Acids in Living Things Lichens, which consist Acids in Precipitation of fungi and algae, living Rain, sleet, or snow together, contribute that contains more chemical weathering acid than normal • Acids in Groundwater (forming a karst feature, known as a cavern)

32. Three Sources of Weak Acids • Acid Precipitation – rain, sleet, or snow that contains a high concentration of acid. Normal precipitation is acidic, acid precipitation contains more acid than normal. • Acids in Groundwater – carbonic acid or sulfuric acid reacts with rocks in the ground, causing a chemical reaction, eating away at the rock. • Acids in Living Things – Lichens produce acids that slowly break down rock.

33. Agents of Chemical WeatheringThese agents weaken the bonds between mineral grains of the rock.

34. Water Can cause rock to be broken down and dissolve. Can take thousands of years to take place.

35. AIR The process of oxidation is a chemical reaction in which an element (for example iron) combines with oxygen, causing rust.

36. Acid Precipitation (weak acid) Rain, sleet, or snow that contains a high concentration of acid. Normal precipitation is acidic, acid precipitation contains more acid than normal.

37. Acids in Groundwater(weak acid) Carbonic acid or sulfuric acid reacts with rocks in the ground, causing a chemical reaction, eating away at the rock. This is a karst landscape.

38. Acids in Living Things (weak acid) Lichens produce acids that slowly break down rock by chemical means.

39. Summary • Wind, water, and gravity cause mechanical weathering by abrasion. • Ice wedging is a form of mechanical weathering in which water seeps into rock cracks and then freezes and expands. • Animals and plants cause mechanical weathering by turning the soil and breaking apart rocks. • Water, acids, and air chemically weather rock by weakening the bonds between mineral grains of the rock.

40. Quick Check Which of the following things cannot cause mechanical weathering? • A. water • B. acids • C. wind • D. animals

41. Quick Check Which of the following is a type of frost action? • A. abrasion • B. oxidation • C. ice wedging • D. gravity

42. Quick Check Which of the following types of chemical weathering causes a karst landscape, such as a cavern? • A. lichens • B. acid precipitation • C. acids in groundwater • D. water

43. Quick Check How do lichens slowly break down a rock? • A. by abrasion • B. by mechanical means • C. by ice wedging • D. by chemical means

44. Quick Check Which of the following will most likely experience oxidation? • A. tennis ball • B. aluminum can • C. wooden fence • D. Bicycle tire

45. The grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles Rain, sleet, or snow that contains a high concentration of acids The process by which rocks break down as a result of chemical reactions The breakdown of rock into smaller pieces by physical means A chemical reaction in which an element, such as iron, combines with oxygen to form an oxide The process by which rock materials are broken down by the action of physical or chemical processes a. mechanical weathering b. oxidation c. weathering d. acid precipitation e. abrasion f. chemical weathering Quick Check

46. Rates of Weathering • What is differential weathering? • How does surface area affect the rate of weathering? • How does climate affect the rate of weathering? • Why do mountaintops weather faster than rocks at sea level?

47. Differential Weathering • Differential weathering is a process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind. • Hard rocks weather more slowly than softer rocks.

48. Devils Tower Devils Tower appears as it does today because of differential weathering. As surrounding rock was worn away, the hard rock of the tower was exposed.

49. The Shape of Rocks • Weathering takes place on the outer surface of rocks. • The more surface area exposed to weathering, the faster the rock will be worn down. • As the surface area increases, the rate of weathering also increases. • If a large rock is broken into smaller pieces, weathering of the rock happens much faster. • The rate of weathering increases because a smaller rock has more surface area to volume than a larger rock. • More of the smaller rock is exposed to the weathering process.

50. Total Surface Area to Volume